It is well-known that during the operation of coke ovens producing metallurgical coke from coking coal, deposits are formed on the equipment and in the ducts and pipes carrying the effluent gases and vaporized liquids, including tar, light oil, and ammonia liquor. Some of the specific products refined from coke ovens include ammonium sulfate, benzene, toluene, xylene, naphthalene, pyridine, phenanthrene, anthracene, creosote, road tars, roofing pitches and pipeline enamels, along with higher aromatic homologues and many other products. Several hundred individual compounds have been found of saturated and unsaturated aliphatics, aromatics, phenols, amines, and heterofunctional compounds of many types.
A simplified description of the coking process would be the destructive distillation of a complex carbonaceous mineral. The compounds formed or driven off during the process have a wide range of boiling and melting points and solubilities, causing the selective condensation or crystallization of the higher boiling compounds with consequent plugging of transmission lines, poor flow and all of the associated difficulties and dangers associated with this problem.
In particular, the refractory-lined standpipes and goosenecks leading to the horizontal collecting main which conduct the volatile products to the chemical recovery plant are most likely to be plugged by these deposits.
A method of preventing this plugging is thus very desirable. One such method we have found is by the introduction of certain very powerful solvents into the system, which dissolve these deposits and tend to maintain them in the vapor stream.
In general, we have found that solvents with a high Solubility parameter as discussed in Kirk-Othmer's Encyclopedia of Chemical Technology, 3rd Ed., Wiley & Sons, N.Y. 1983, Vol. 21, pp. 377-401 are especially effective. These include N-methyl-2-pyrolidone, N, N-dimethylformamide, 1,4 dioxane, butyrolactone, and other high boiling powerful solvents.